66 C2 DOT#5 Brake fluid "disappears" during Winter Storage

[Larry E.]

All I know is I have two C2 Corvettes with identical brake systems although with different
types of brake fluid. Both are stored in identical ways. (Non-Heated building in Car Bags)
for a year or more at a time. Temps and Humidity vary a lot since In Illinois we have temps
over 100 and -10 degrees for the year. Both car results when taken out of the bag in the
Spring are the same. Brake Fluid must be added to both but once added no more is needed
for the 5 month Summer use. Would like to hear from someone else that stores their cars
like me with the similar degrees on the outside of their building. Thanks for all the comments.
Larry

[Mark F.]

Larry,

a few data points regarding brake fluid and water - not an answer to your question; but as others have already commented - at least elimination of one hypothesis IMO

Brake fluid vapor pressure is almost non-existent: < 0.01 mmHg @68° F
By comparison, water vapor pressure @ 68° is roughly 17.5 mmHg (~ 1,750 x higher than Brake Fluid) and almost 50mmHg @ 100°F ! (~ 5,000 x higher than Brake Fluid)
So, your brake fluid is NOT evaporating anywhere near the losses you're seeing, IMO.

Also, your white pellets are probably calcium chloride (used as a desiccant).
It does not cause water (nor does anything else other than HEAT) to evaporate at a higher rate - it simply adsorbs the vaporized state of water (AKA humidity) from the air, which then goes into solution w/ the salt (deliquescence).
Kind of like when you leave leftover rock salt (sodium chloride) in your garage over the summer and it gets all caked up and gooey.
So, your "weed killer" is probably just a high concentration of salt water

[Larry E.]

Thanks Mark for nice response. Now:
There must be some people on the board that use "Car Bags" to store their vehicles
during the Winter or longer storage. I believe that there will be many more going this
route in the future. To heat and dehumidify a building is getting to the point of excessive
cost. Just got my Ameren Utility bill in and was the highest I ever got.(For my house) There are people
I know with bigger houses and different Furnace/A-C systems that are getting billed
for $700 per month in Illinois. And this can get only worse. JMHO-Larry

[Duke W.]

Larry,

a few data points regarding brake fluid and water - not an answer to your question; but as others have already commented - at least elimination of one hypothesis IMO

Brake fluid vapor pressure is almost non-existent: < 0.01 mmHg @68° F
By comparison, water vapor pressure @ 68° is roughly 17.5 mmHg (~ 1,750 x higher than Brake Fluid) and almost 50mmHg @ 100°F ! (~ 5,000 x higher than Brake Fluid)
So, your brake fluid is NOT evaporating anywhere near the losses you're seeing, IMO.

Also, your white pellets are probably calcium chloride (used as a desiccant).
It does not cause water (nor does anything else other than HEAT) to evaporate at a higher rate - it simply adsorbs the vaporized state of water (AKA humidity) from the air, which then goes into solution w/ the salt (deliquescence).
Kind of like when you leave leftover rock salt (sodium chloride) in your garage over the summer and it gets all caked up and gooey.
So, your "weed killer" is probably just a high concentration of salt water

Excellent data and analysis. I agree that the brake fluid loss is not from vaporization. It has to be leaking, maybe from multiple locations. I can't think of any other rational explanation.

As most may know liquids cannot exist in a vacuum like outer space. Since all liquids have a vapor pressure they will eventually evaporate in a vacuum, but the lower the vapor pressure, the longer it takes. With a vapor pressure of less than 0.01 mm Hg at room temperature and sea level atmospheric pressure, an ounce to two in a small cup would likely take years to completely evaporate

Duke

[Bob S.]

Larry - Have you checked the rod leading from the brake pedal to the master cylinder right after storage. If its wet at all you may have leak out of the back of the master cylinder. I have seen this and there was no evidence on the carpet or insulation. Many years ago I read a post recommending to pump the brakes at least once a month to avoid silicone brake fluid leakage and it has worked very well for me. I pump at least once a month year-round.

[Larry E.]

Bob: Thanks for your comments. Please read my #31 thread. THERE IS NO LEAK IN MY
SYSTEM AS WE THINK OF TRADITIONAL LEAKS. My belief until I hear a better one is that
in a year or more time in a bag with all the variable temps/humidity the caliper seals
shrink and expand ever so slightly. With the brake pedal not being used this lets out
some brake fluid in the form of VAPOR/LIQUID IN A SMALL AMOUNT AT A TIME. Then it is
absorbed and finds it way into the (3)containers which have "Dry-Z-Air" white pellets
in them at the beginning of storage. When car is taken out of the bag the three con-
tainers are completely full of a liquid substance which Mark explained above. There is
no evidence of any liquid on the bags floor(when car is taken out of the bag) that there was a "traditional leak".
Thanks-Larry

[Larry E.]

Excellent data and analysis. I agree that the brake fluid loss is not from vaporization. It has to be leaking, maybe from multiple locations. I can't think of any other rational explanation.

As most may know liquids cannot exist in a vacuum like outer space. Since all liquids have a vapor pressure they will eventually evaporate in a vacuum, but the lower the vapor pressure, the longer it takes. With a vapor pressure of less than 0.01 mm Hg at room temperature and sea level atmospheric pressure, an ounce to two in a small cup would likely take years to completely evaporate

Duke

Hay Duke: Not sure that brake fluid does not evaporate even though at a much slower rate.
I have taken 3 coffee cups with one filled with gas;one with anti-freeze;and one with brake fluid.
Pour the 3 cups (4 feet apart) on your WARM concrete driveway in the Summer. ALL THREE WILL DISAPPEAR IN DUE TIME WHICH DOES NOT take a A LOT OF TIME. WHERE I COME FROM THIS IS CALLED
EVAPORATION. LARRY P.S. When my cars are in the sealed "Car Bags" the interior of the bag
is not at "Room Temperature".